Mannanase is a promising enzyme for decomposing a mannan component that constitutes hemicellulose. Hemicellulose is a constituent component of the plant cell wall containing cellulose associated with lignin and a polysaccharide most abundant in the nature next to cellulose. Hemicellulose includes mannan materials such as galactomannan and arabitogalactan contained in the seed of leguminous plants, or glucomannan and galactogluromannan of coniferous trees. The most important availability of mannanase that is included in hemicellulase together with xylanase and glucanase is saccharifying hemicellulose, which is a recyclable plant resource in the earth, into a carbon source available to organisms. But, this use of mannanase is not put into practice yet. Presently, hemicellulase is useful in industrial applications including food processing of coffee, cocoa, tea, cereal, etc. and manufacture of pulp.
When processed with hemicellulase, grains that contain hemicellulose used for foods or feeds are converted to a form adequate for foods or feeds with an improved energy yield and a deterioration of viscidity. With an increase in the energy content of foods or feeds, it is advantageous, especially for feeds, to reduce the cost for breeding of domestic animals.
Soybean proteins are used as feeds for domestic animals such as dogs, cats, pigs, fish, fowls, or the like. Although not a principal energy source, the soybean meal is an excellent protein source containing essential amino acids. About 10% of carbohydrates as an energy source in the soybean meal are galactan and pentosan. A large amount of these carbohydrates are not digested by the monogastric animals but excreted. Mannanase decomposes galactan out of the carbohydrates of the soybean meal into a low-molecular oligosaccharide or monosaccharide that can be readily digested by the unit animals.
Mannanase is produced by microorganisms such as mold or yeast fungus as well as Bacillus subtilis, Aeromonas, Enterococcus, Pseudomonas, and Streptomyces. Some higher plants or animals can produce mannanase. Microorganisms used for production of the mannanase are usually Trichoderma or Aspergillus sp. fungal strains. Fungus-originated mannanase has the maximum activity in the acidic condition. Although different by portions in the physiological condition of the digestive organs of pigs or fowls, the pH condition of the digestive organs after the small intestine affected by the mannanase is around 6.5. Accordingly, the enzyme for feed additives is composed of mannanase, which is highly active in the neutral medium, rather than the fungus-originated mannanase having a high activity in the pH range of 3.6 to 5.5.
In general, there are three known enzymes, i.e., endo-β mannanase, exo-β mannanase and β-mannosidase that participate in the complete decomposition and conversion of the mannan, which is a principal component of hemicellulose. Endo-β mannanase catalyzes at random the hydrolysis of the β-D-1,4-mannopyranosyl bonds of mannan polysaccharides having a higher polymerization degree than mannotetraose that has a mannose polymerization degree of 4. The present invention places great importance on the first enzyme, i.e., endo-β mannanase, which will be hereinafter referred to as “mannanase”.
The inventors of this invention isolated from the soil a novel Bacillus sp. WL-1 strain that produces mannanase, which is highly active in the neutral and the acidic media, and found out that the isolated and identified Bacillus sp. WL-1 strain produces a lot of mannanase in a culture medium containing lactose and wheat bran.